1. Field of the Invention
The present invention relates to a plasma etching method and apparatus, and more particularly to a plasma etching method and apparatus which are well suited for etching the samples of semiconductor device substrates, etc.
2. Description of the Prior Art
In recent years, the microfabrication of patterns has rapidly proceeded with the heightened densities of integration of semiconductor devices.
As techniques for precisely etching a microscopic pattern of about 1 .mu.m, it has heretofore been practised to control ion energy which is incident on a sample.
The techniques are known from Japanese Patent Laid-open No. 13625/1986, Japanese Patent Publication No. 41132/1986, and so on. These techniques are claimed to be effective for the etching of the microscopic pattern of about 1 .mu.m and the formation of a film of high quality.
At present, as a technique for etching a pattern which is still minuter than the conventional pattern of about 1 .mu.m, there is known a process (hereinbelow, termed "low-temperature etching") wherein a sample holder is furnished with a cooling device, and a sample is cooled to a temperature not higher than 0.degree. C. which is a minimum temperature of water and then etched as disclosed in, for example, Japanese Patent Laid-open No. 158627/1985. According to this process, the reactions between a solid and neutral particles such as radicals are suppressed, and the amount of side etching or lateral etching at a side wall can be made very small without lowering an etching rate in the depth direction of the sample. The low-temperature etching is therefore claimed to be effective for the etching of the microscopic pattern.
As referenced concerning the low-temperature etching of this type, there are mentioned, for example, Japanese Patent Laid-open No. 128630/1988 No. 115338/1988 and No. 174322/1988, all of which disclose cooling a sample to a temperature not higher than 0.degree. C. which is a minimum temperature of water.
The first-mentioned technology of controlling the ion energy has the feature that, when the ion energy is increased, sputter etching based on ions takes place mainly, so an anisotropic etching process becomes possible. On the other hand, however, there arise the problems that the sample is heavily damaged due to ion bombardment and that the ratio of selectivity of a material to be etched to the subbing layer thereof becomes small.
To the contrary, when the ion energy is decreased, an etching process which suffers from no damage and which affords a high selectivity ratio becomes possible. On the other hand, however, the amount of the sputter etching based on the ions decreases, and hence, the period of time of etching lengthens, resulting in the problem that the period of time of isotropic etching based on neutral particles such as radicals prolongs so as to side-etch the sample. It has accordingly been difficult to apply the technology to the etching process of a pattern which is further minified.
The low-temperature etching technology is very effective for etching the still minuter pattern at a good anisotropy. The inventors' experiment for a higher practicability, however, has revealed that a problem to be stated below is involved in the performance of the low-temperature etching.
When the sample is cooled to the low temperature and then subjected to the etching process, the reactions between the neutral particles and the solid are suppressed, and the etching weakens. Thus, some materials to be etched give rise to residues on surfaces to be etched in such a manner that a substance which ought to react with the material to be etched and then vaporize as a reaction product adheres and remains on the surface to be etched, or that the material to be etched remains unetched.
Related to the present invention are U.S. Pat. Nos. 4,622,094 and 4,795,529.